Obesity, resulting from excess storage of triacylglycerol in adipose tissue, is a major worldwide health epidemic, associated with pathological disorders such as diabetes, hypertension and atherosclerosis. As sensors for lipids, nuclear hormone receptors (NHRs) play a key role in regulating adipose tissue metabolism. NHRs do not act alone but rather via recruitment of co- factors (co-repressors and co-activators) that serve as mediators of the hormone signal. NCoR and silencing mediator of retinoid and thyroid hormone receptors (SMRT) are the most well studied co-repressors and play a key role in NHR signaling. Mice with a mutation in the SMRT gene exhibit increased adiposity and widespread metabolic defects, implicating SMRT as a crucial factor in regulating adipocyte metabolism. However, the role of NCoR specifically in adipose tissue has not been investigated. NCoR may play a critical role in controlling adipocyte metabolism by regulating a unique subset of genes in this tissue. Furthermore, lack of both co- repressors in adipose tissue may result in a more pronounced phenotype than lack of either alone. Extensive examination of co-repressor action in adipose tissue will enhance our understanding of adipose tissue biology and be important in designing novel therapeutic targets for the treatment obesity and related metabolic disorders. Aim 1 of this proposal will assess the in vivo role of NCoR in adipose tissue by examining mice lacking NCoR specifically in this tissue. It will also determine the function of both co-repressors in adipose tissue, by characterizing mice lacking both NCoR and SMRT in adipose tissue. Aim 2 will capitalize on the availability of high context whole genome sequencing and advances in methods for chromatin immunoprecipitation to define the binding sites of NCoR and SMRT in adipocytes. It will also establish the gene expression signatures of NCoR and SMRT in mature adipocytes isolated from co-repressor deficient mice through use of RNA-Sequencing. Aim 3 will confirm the specific NHRs that NCoR regulates in adipose tissue through use of luciferase reporter gene assays and lentiviral NHR- specific shRNA knockdown in NCoR deficient adipocytes. Generation of novel genetic mouse models combined with next-generation sequencing and genome-wide approaches to reveal transcriptional outcomes will reveal the molecular mechanism underlying NCoR action in adipose tissue and help to illuminate many of the unknowns regarding the actions of co-repressors.